Switch to Jednotka template, discarding old styles.

The Jednotka template is much prettier, but more importantly, it saves
me from HTML/CSS work I find unrewarding. Jednotka is implemented with
Compass/Sass, and has a powerful _variables partial we can tweak to get
great results. Its four-column portfolio view should be fine for most
video lists, and we can get fancier if we ever need to (such as table
views for the admin).

Updated templates.cljs to take advantage of the new template styles.

Add Jednotka template HTML, and implement home template.

Add Jednotka theme styles and images, removing old ones.

Use symlinked jednotka_active.scss; see changes to README.md. Also added
Jednotka active style symlink to .gitignore.